There is a need especially in automated mailing systems to fold sheet stock in half with the side benefit that other materials can be inserted within the folded sheet. Prior art sheet folding machines are very complicated and expensive and are extremely large machines that are only capable of folding a certain size sheet. Such prior art machines teach the general concepts of continuous sheet feeding as well as lifting the sheet leading edge and holding it until the trailing edge is conveyed beneath it. However, these prior art devices are not readily adaptable to various sheet widths. Additionally these known devices utilize actuators which rely on outside energy sources to lift and grip the sheet lead end.
For example, U.S. Pat. No. 3,517,919 to Flygare discloses a sheet folding machine that incorporates a lead edge lifting device incorporating lift fingers which are actuated with pneumatic pistons and which grab the sheet lead edge upwards to be pinched between gripping elements. The lifting device of Flygare relies upon a complex system of switches and valves to insure that the lead edge of the sheet is gripped and released at a proper time. Flygare contains no teaching or suggestion regarding the ability to nest inserts for the sheet and Flygare describes a second folding operation which would prevent the inclusion of such inserts.
U.S. Pat. No. 2,861,801 to Cran discloses a lead edge lifting device used for a laundry folder. Three switch elements monitor the advance of the lead edge and a movable gripping member is actuated to intercept the oncoming lead edge. The lead edge is gripped between the movable grip and a fixed grip until the proper time passes to accomplish folding the sheet in half. Another patent to Cran U.S. Pat. No. 2,815,946 is concerned with a safety catch mechanism which is employed to insure that the movable grip does not accidentally drop onto the conveyor until the sheet trailing edge has passed under it.
U.S. Pat. No. 4,875,668 issued to Spyra and assigned to the assignee of the instant application, discloses high speed sheet folder and presser for automated mailing systems. U.S. Pat. No. 4,875,668 issued to Spyra is herein incorporated by reference. Spyra incorporates a set of software controlled rods that roll the lead edge of the paper up and back over the trailing half of the paper, thus enabling the machine to run continuously and providing the capability of folding any length of paper. However the apparatus of Spyra is unable to handle paper of universal width without breaking the transport, thus adding to the cost and complexity of the machine.
Accordingly, there is a need for a continuous sheet folder that can fold any size sheet (length and width) in half, with or without nested inserts inside the folded sheet. The present invention fulfills this need and overcomes the disadvantages of prior art folding machines.